1. Field of the Invention
The present invention relates to building panels. More specifically, the invention provides an impact resistant exterior building panel having a fabric reinforcing layer and a polymer core between a pair of metal skins.
2. Description of the Related Art
The need for reinforced building panels in regions that are subject to hurricanes and other storms capable of significantly damaging buildings is increasingly recognized. In many areas of the United States, building codes are now requiring commercial and residential structures to be designed to resist the wind loads and debris impact loads generated by these severe storms. Current practice for many of these areas is to sheath the exterior surface of the structure with minimum ⅝ inch thick plywood, before application of the final building exterior covering. For example, wall panels in Florida that use composite building panels having metal skins and polymer cores are typically installed over ⅝ inch (1.588 cm) thick 5-ply plywood to meet the debris impact load requirements specified by the Florida building code. Although the plywood provides excellent impact resistance, its installation increases costs and build time for the structure. The wall sections also are heavy, and the wood adds fuel content to the system, decreasing the overall fire resistance of the structure. There exists a need to improve the impact resistance of these metal composite material building panels, to meet the impact requirements for severe storm resistance, without the use of the plywood sheathing.
Methods to improve the impact resistance for metal composite panels for uses other than building panels are described in other patents. For example, U.S. Pat. No. 5,092,952 issued to M. G. Minnick et al. on Mar. 3, 1992, discloses a composite panel having an aluminum skin and a glass fiber reinforced polypropylene core. The skin is laminated to the core using an adhesive having an ethylene/acrylic acid copolymer combined with a linear low density polyethylene or a thermoplastic styrene/diene block copolymer. Similar inventions are described in U.S. Pat. No. 5,246,523, issued to M. G. Minnick et al. on Sep. 21, 1993, U.S. Pat. No. 5,248,367 issued to M. G. Minnick et al. on Sep. 21, 1993 and U.S. Pat. No. 5,248,369, issued to M. G. Minnick et al. on Sep. 28, 1993. Reinforcement of these panels is provided by the continuous dispersion of the reinforcing fibers within the polymer core as it is being produced. This type of reinforcement would not provide the same impact resistance as a panel having a reinforcing layer directly adjacent to the outer skin. Furthermore, production of these panels is more cumbersome.
Similar approaches to continuous dispersion of fibers into a polymer core of a metal composite are described in U.S. Pat. No. 6,586,110, issued to D. F. Obershaw on Jul. 1, 2003. This patent discloses composite structural members having exterior and interior skins that may be made from metallic sheet, with a core having a ribbed structure and a resinous or polymeric filler therein. In some embodiments, sheet molding compounds are used for the inner or outer portions, and may be reinforced with KEVLAR® fibers. The rib structure within the core precludes the use of manufacturing procedures that could be used without such a ribbed core.
Approaches to improving the adhesion of the metal skins to the polymer cores of metal composite material are described in other patents. One example is U.S. Pat. No. 6,855,432, issued to S. Hobajar, et al. on Feb. 15, 2005, disclosing an adhesive composition that is particularly useful for joining aluminum skins to polymer cores to form composite panels. No method of reinforcing a panel is disclosed.
Approaches to bonding parallel aramid fibers inside aluminum sheets with various adhesive systems are also described in the art. These materials were designed to provide high performance aerospace materials for use in wing skins and other aerodynamic control surfaces and are detailed in patents such as EP 0056289-B1; U.S. Pat. Nos. 4,029,838; 4,500,589; and 5,227,216. None of these are directed at providing the impact improvements needed for typical metal composite building panels to meet the requirements for use in storm prone areas.
Accordingly, there is a need for an improved building panel for use in storm prone regions that offers improved impact resistance without increasing the weight of the panel or compromising the fire retardation properties of the wall system. There is a further need for a building panel having good adhesion between the outer metal skin and interior core components, and which is easy and inexpensive to manufacture.